[6.0] IRGen: Rename the section pointing to rodata of generic classes to __objc_clsrolist

Also emit it per default.

This is to enable rewriting method lists in generic class' metadata
pattern by the linker to the relative format.

Relative method lists are very important for pointer security.

Risk: Very low. We emit an extra section containing pointers. No one
currently consumes this section.

rdar://129299739
(cherry picked from commit f063c7e)

Author: aschwaighofer

include/swift/AST/IRGenOptions.h

@@ -554,7 +554,7 @@ class IRGenOptions {
         EnableGlobalISel(false), VirtualFunctionElimination(false),
         WitnessMethodElimination(false), ConditionalRuntimeRecords(false),
         InternalizeAtLink(false), InternalizeSymbols(false),
-        EmitGenericRODatas(false), NoPreallocatedInstantiationCaches(false),
+        EmitGenericRODatas(true), NoPreallocatedInstantiationCaches(false),
         DisableReadonlyStaticObjects(false), CollocatedMetadataFunctions(false),
         ColocateTypeDescriptors(true), UseRelativeProtocolWitnessTables(false),
         UseFragileResilientProtocolWitnesses(false),

lib/IRGen/GenDecl.cpp

@@ -1167,9 +1167,9 @@ void IRGenModule::emitGlobalLists() {
     if (IRGen.Opts.EmitGenericRODatas) {
       emitGlobalList(
           *this, GenericRODatas, "generic_ro_datas",
-          GetObjCSectionName("__swift_rodatas", "regular"),
+          GetObjCSectionName("__objc_clsrolist", "regular"),
           llvm::GlobalValue::InternalLinkage, Int8PtrTy, /*isConstant*/ false,
-          /*asContiguousArray*/ true, /*canBeStrippedByLinker*/ true);
+          /*asContiguousArray*/ true, /*canBeStrippedByLinker*/ false);
     }
 
     // Objective-C class references go in a variable with a meaningless

test/IRGen/generic_class_rodata_list.swift

@@ -30,7 +30,7 @@
 // CHECK:         .quad   0
 // CHECK:         .quad   __CLASS_METHODS__TtC25generic_class_rodata_list9Somethin
 
-// CHECK:        .section        __DATA,__swift_rodatas
+// CHECK:        .section        __DATA,__objc_clsrolist
 // CHECK:        .p2align        3
 // CHECK:_generic_ro_datas:
 // CHECK:        .quad   ___unnamed_1+40